A financial printer, such as that used in banks' automatic teller machines (ATMs), uses a roll of supply paper for dispensing receipts to customers. These paper supply rolls are periodically marked on one edge thereof with black marks. These black marks define the length of the printed receipt that is dispensed to the banking customer. Optical sensors in the printing system detect the black marks, and generate signals to instruct the cutting mechanism to cut the paper to the appropriate receipt length.
Despite the fact that the sensing and dispensing systems of ATMs are fairly simple in their concept, the machines' lack of reliability and repeatability in achieving adequate receipt lengths is problematical. One of the major causes of this problem is the fact that banks use paper rolls from different manufacturers and supply vendors; hence, they are not manufactured according to a set standard. The optical characteristics thereof thus have a wide tolerance variation, i.e., the surface and the black markings of these different papers each have their own optical properties of reflectivity and light absorption, depending on the manufacturer.
Typically, state-of-the-art sensing systems in printing machines use optical devices consisting of an infrared light-emitting diode (LED) with a focused, major axis beam. The beam is reflected from the rolled paper into a photosensitive device, such as a photo-transistor. The reflectivity from the white surface of the paper excites the base of the transistor, allowing it to conduct current. While the transistor is conducting, the dispensing mechanism continues to advance the paper. The advancement of the paper ceases when the transistor current falls to a level that indicates that a black mark has come into the range of the LED. When this occurs, the infrared, major axis beam of the LED is absorbed by the black mark; thus, the light is not reflected back towards the photo-transistor, and the transistor ceases to conduct current at a level that is associated with white paper.
Also contributing to the problem concerning reliability and repeatability are: production tolerances associated with optical sensors; the length of the gap between the paper and the LED; the length of the gap between the paper and the sensor; LED light output variations; photo-transistor sensitivity variations; and circuitry parameters.
One of the objectives of this invention is to fabricate an improved sensing and dispensing system for financial and retail receipts that is reliable and repeatable, despite any variation in optical characteristics of paper supply rolls.
Another objective of the invention is to automate the calibration process of retail and financial printers, whereby the system becomes self-adjusting and thus eliminates manual adjustments.
Still another objective of this invention is to provide an optical system that is fabricated from inexpensive components, ones that can adapt to a wide variation in optical characteristics of the supply roll media.
The present invention provides for a simplified, self-adjusting and easily calibrated optical sensing system for providing a printed receipt from a financial or retail printing device.
The current invention eliminates the need, prior to the calibration process, to accurately position a black mark on a supply roll in the range of an optical sensor.
The improved optical sensing system of this invention adjusts for different ambient lighting conditions, component variations and tolerances, as well as optical characteristics of black marks and varying supply roll media.
The sensing system of this invention eliminates or greatly reduces variations in the optical sensing due to dust build-up.
The optical sensing system of this invention eliminates the need for special tools or requisite adjustments to conform or adjust the optical characteristics of the black marks or the paper reflectivity qualities to the optical sensing system.